My third Amiga 4000 sound problem

[Deling]

Hi i have problem with sound in my third backup mobo 4000
all caps replace , audio area look very good
sound exist but is very very low and I hear hard disk drive and fan in loudspeaker
transistor mpf102 replaced too and nothing !!

what can I do ? new lf347m ?

 

[hooverphonique]

Have you verified voltages on all active components of the audio circuit?

also, hard drive and fan noise was probably always there, you just notice it because you have to turn the volume up a lot.

 

[hese]

Probably a problem either in the U402, U403 or supporting components or traces. Do the traces and components around that area have corrosion? Can you post a picture?

But first better verify the voltages as hooverphonique suggested.

 

[Deling]

corrosion very little ! cleaned with izo , traces look great I checked with multimeter , atx give -11.30v on A4000d psu conector , are you suspect lf347m and lm8333?

 

[hese]

Check the voltages of each pin of the U402. They all should be around +2.5V except +12V on pin 4 and -12V on pin 11.

 

[Deling]

I checked u402 2.37v there are ok , pin4 12v and -11.37 on pin 11

but i checked LM833 too and there are very strange V , V are other like in this thread
http://amiga.serveftp.net/audio_repair.html

 

[Deling]

which LM833M exactly I have to buy? could someone help me with choice this chip ? there are many version chip , I dont know which will be good for Amiga mobo

 

[Deling]

hurrraa problem repaired !!! !!! there was problem with track corrosion ! thank you HESE
and thank this http://www.amigapcb.org
PCB website for many hours with lupe and solder machine ! I found one small problem fast connect jumper with wire and sound is great !! amazing

 

[hese]

Great job, good to hear you got it working.